AT&T bans port 25 as well so you cannot run a SMTP server, they do that to cut down on spam.

I remember my son was in an out of town Soccer game, and we stayed in a hotel. One of the other families brought their XBox 360 and tried to plug it into the Ethernet port and unplug the custom game console controller that rented Nintendo 64 games and plug the XBox 360 into their TV set. For some reason their Internet blocked access to the ports that the XBox 360 used to sign in and play games so they couldn't play anything. I guess they wanted to force people to rent N64 games on their custom video game console controller?

If enough ISPs block port 8333, the Bitcoin programs will have to be changed to be like the Bittorrent clients to use a random port and connect via a tracker or something to that port.